1. Technical Field
This invention relates generally to a cover for an open tank and more particularly to a sealable, substantially flat tank cover comprising a plurality of self-supporting interlocking panels.
2. History of Related Art
Sealed covers are frequently required to enclose open waste water treatment tanks, potable water tanks, gas or crude oil processing and storage tanks, drilling fluid tanks, chemical waste treatment tanks, and similar tanks used to store or process gas or odor generating fluids or sludge. The term "tank" is used herein in a generic sense, and includes above ground level tanks, below ground level basins, and combinations of above and below ground level structures. Generally, since such storage tanks have a relatively large open surface area across the top of the tank, the cover for the tank also has a relatively large surface area and is thus typically assembled in the field, desirably directly on the tank itself.
For example, sealed tank cover structures are described in U.S. Pat. No. 5,325,646, issued Jul. 5, 1994, to Jeffrey A. and John Hallsten, and U.S. Pat. No. 5,617,677, issued Apr. 8, 1997, to Jeffrey A. Hallsten. The tank cover structure described in both of the Hallsten patents uses a series of cross members to support a plurality of panels that are attached to and supported by the cross members. During assembly, the panels are arched to provide sufficient structural support for the structure. Because the panels are assembled over an open tank, they are difficult to position and bend to provide the desired arch shape, and support members remain in or over the tank after removal of the panels. Also, the individual panels are not easily gripped and moved or placed. Moreover, the flexure characteristics of the individual panels, necessary to provide the arched structure when installed, significantly increases field assembly problems. Additionally, arched structures do not provide a desirable planar walking surface. Arched or domed walking surfaces are particularly disadvantageous in cold climates where the cover may be subjected to a coating of snow or ice.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a sealed cover for an open tank that has a flat walking surface. It is also desirable to have such a cover that is comprised of a plurality of separately positionable self-supporting panels extending across the width of the tank. Furthermore, it is desirable to have such a tank cover wherein each of the individually positionable panels has a readily accessible handle provided at the end of each panel which is moveable to a position substantially flush with the walking surface of the cover when not required for lifting or moving the panel.